examples/src/main/java/org/apache/spark/examples/streaming/JavaCustomReceiver.java
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.examples.streaming;

import com.google.common.io.Closeables;

import org.apache.spark.SparkConf;
import org.apache.spark.storage.StorageLevel;
import org.apache.spark.streaming.Duration;
import org.apache.spark.streaming.api.java.JavaDStream;
import org.apache.spark.streaming.api.java.JavaPairDStream;
import org.apache.spark.streaming.api.java.JavaReceiverInputDStream;
import org.apache.spark.streaming.api.java.JavaStreamingContext;
import org.apache.spark.streaming.receiver.Receiver;
import scala.Tuple2;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.ConnectException;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.regex.Pattern;

/**
 * Custom Receiver that receives data over a socket. Received bytes is interpreted as
 * text and \n delimited lines are considered as records. They are then counted and printed.
 *
 * Usage: JavaCustomReceiver <master> <hostname> <port>
 *   <master> is the Spark master URL. In local mode, <master> should be 'local[n]' with n > 1.
 *   <hostname> and <port> of the TCP server that Spark Streaming would connect to receive data.
 *
 * To run this on your local machine, you need to first run a Netcat server
 *    `$ nc -lk 9999`
 * and then run the example
 *    `$ bin/run-example org.apache.spark.examples.streaming.JavaCustomReceiver localhost 9999`
 */

public class JavaCustomReceiver extends Receiver<String> {
  private static final Pattern SPACE = Pattern.compile(" ");

  public static void main(String[] args) throws Exception {
    if (args.length < 2) {
      System.err.println("Usage: JavaCustomReceiver <hostname> <port>");
      System.exit(1);
    }

    StreamingExamples.setStreamingLogLevels();

    // Create the context with a 1 second batch size
    SparkConf sparkConf = new SparkConf().setAppName("JavaCustomReceiver");
    JavaStreamingContext ssc = new JavaStreamingContext(sparkConf, new Duration(1000));

    // Create an input stream with the custom receiver on target ip:port and count the
    // words in input stream of \n delimited text (e.g. generated by 'nc')
    JavaReceiverInputDStream<String> lines = ssc.receiverStream(
      new JavaCustomReceiver(args[0], Integer.parseInt(args[1])));
    JavaDStream<String> words = lines.flatMap(x -> Arrays.asList(SPACE.split(x)).iterator());
    JavaPairDStream<String, Integer> wordCounts = words.mapToPair(s -> new Tuple2<>(s, 1))
        .reduceByKey((i1, i2) -> i1 + i2);

    wordCounts.print();
    ssc.start();
    ssc.awaitTermination();
  }

  // ============= Receiver code that receives data over a socket ==============

  String host = null;
  int port = -1;

  public JavaCustomReceiver(String host_ , int port_) {
    super(StorageLevel.MEMORY_AND_DISK_2());
    host = host_;
    port = port_;
  }

  @Override
  public void onStart() {
    // Start the thread that receives data over a connection
    new Thread(this::receive).start();
  }

  @Override
  public void onStop() {
    // There is nothing much to do as the thread calling receive()
    // is designed to stop by itself isStopped() returns false
  }

  /** Create a socket connection and receive data until receiver is stopped */
  private void receive() {
    try {
      Socket socket = null;
      BufferedReader reader = null;
      try {
        // connect to the server
        socket = new Socket(host, port);
        reader = new BufferedReader(
            new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8));
        // Until stopped or connection broken continue reading
        String userInput;
        while (!isStopped() && (userInput = reader.readLine()) != null) {
          System.out.println("Received data '" + userInput + "'");
          store(userInput);
        }
      } finally {
        Closeables.close(reader, /* swallowIOException = */ true);
        Closeables.close(socket,  /* swallowIOException = */ true);
      }
      // Restart in an attempt to connect again when server is active again
      restart("Trying to connect again");
    } catch(ConnectException ce) {
      // restart if could not connect to server
      restart("Could not connect", ce);
    } catch(Throwable t) {
      restart("Error receiving data", t);
    }
  }
}
